D-Programming-Language/dmd — pull request #3075 by leandro-lucarella-sociomantic (2014-01-09 15:03:13+00:00)
Title: ini: Add support to define undefined variables

Similarly to Make files, the syntax `VAR ?= value` is added to define
variables only when they were previously undefined.

In this case, if the environment variable `VAR` was undefined, then it
will be defined with the value `value`, otherwise the previous content
of `VAR` will be preserved.

This is useful to define default flags in the config file that can be
easily overridden by using environment variables.

This comes with a bug-fix and some updates improvement to the config
file man page too.

Soon a pull request for the master branch...